A slurry of 300 mg (0.73 mmol) (2S,4R)-methanesulfonic acid 1-methanesulfonyl-4-(4-methoxy-benzylsulfanyl)-pyrrolidin-2-ylmethyl ester and 109 mg (0.73 mmol) of NaI in 3 ml DMF at 0° C. was treated with 0.35 ml (2.93 mmol) benzylmercaptane and 96 mg (2.2 mmol) 55% NaH. The reaction was warmed up during 2 h to room temperature and worked up with aqueous saturated NH4Cl solution/EtOAc (3×). The organic phase was dried over Na2SO4, evaporated and purified by crystallization (Et2O) to give 158 mg (49%) of (2S,4R)-2-benzylsulfanylmethyl-1-methanesulfonyl-4-(4-methoxy-benzylsulfanyl)-pyrrolidine, mp 69–71° C., MS: 438 (MH+).
